Recently, a high-output integrated circuit device that mounts an integrated circuit chip including a high-output transistor is demanded for a mobile telephone base station or radar. In such an integrated circuit mounted device, high-output characteristics are realized by arranging in parallel a plurality of power transistors formed on an integrated circuit chip on a metal package and forming an impedance transformer by a line on a dielectric substrate for impedance matching.
In order to form a wideband matching circuit, an impedance transformer is utilized, in which a plurality of ¼ wavelength lines is connected in series so as to keep a Q value small. Such an impedance transformer is used widely in an integrated circuit mounted device that requires wideband characteristics because the wideband characteristics may be obtained by increasing the number of stages of the ¼ wavelength line. When configuring a ¼ wavelength impedance transformer, a transmission line having a desired characteristic impedance is formed with the substrate thickness of the wire, the dielectric constant of the substrate, and the wire width being taken into consideration.
FIGS. 1A and 1B are diagrams explaining impedance conversion, wherein FIG. 1A illustrates a case of matching with one stage and FIG. 1B illustrates a case of matching with two stages. It is assumed that the output impedance of a transistor is R1, the input impedance in the subsequent stage is R0, and R0>R1 holds. When performing matching with one stage as illustrated in FIG. 1A, one ¼ wavelength line having a characteristic impedance Z is used and it is set as Z=(R0×R1)1/2. In contrast to this, when performing matching with two stages as illustrated in FIG. 1B, a ¼ wavelength line having a characteristic impedance Z1 and a ¼ wavelength line having a characteristic impedance Z2 are connected in series and they are set as Z1=(R1×R0)1/4 and Z2=(R1×R03)1/4. There is a case where ¼ wavelength lines in three or more stages are connected in series.
In a high-output integrated circuit mounted device, the gate width of a transistor is increased in order to increase the output. The increase in the gate width of a transistor may be realized by using a plurality of transistors having the same characteristics in parallel and connecting the outputs of the plurality of transistors commonly. If the gate width of the transistor is increased in this manner, the output impedance of the transistor is reduced to 1Ω or less. In order to increase the output of the transistor to the maximum, the output impedance of several ohms is converted into 50Ω used normally and to perform impedance matching. In this case, in order to secure the frequency band, as illustrated in FIG. 1B, a plurality of impedance transformers are connected in series and the impedance is converted into 50Ω stepwise for matching. The shape of the ¼ wavelength line, such as its length and width, is determined based on the dielectric constant, the impedance, etc., of the substrate. Because of this, a high-impedance line that uses a substrate with a low dielectric constant has a longer length and a wider width compared to a low-impedance line that uses a substrate with a high dielectric constant. As a result, there is such a problem that the size of the matching circuit is increased. Because of this, a pattern layout in which a long line is bent in wiring is used to downsize the matching circuit.
On the other hand, due to the recent development of broadband, the demand for large-capacity high-speed radio communication is increasing. It is expected that the third generation of the base station amplifier of a mobile telephone will become widely used in order to deal with a larger capacity and further the fourth generation will develop in the future. The new communication scheme (WiMAX) has been put into practical use and it is expected that an increase in capacity will develop. In such circumstances, a higher output, higher efficiency, wider band, and reduction in cost are demanded. On the other hand, for a radar amplifier, a higher output and wider band to improve performance, such as the extension of detection range and resolution, and further high efficiency to realize reduction in operation cost and downsizing of a cooler is demanded.
Furthermore, in a phased array radar, it is necessary to arrange radar elements including an amplifier in the form of an array in a narrow space, and therefore, further downsizing of an amplifier is demanded.